What do you call a baby sea urchin?

Answer: larva pluteus (free swimming stage), juvenile (young urchin)

A baby sea urchin is called a larva pluteus (free swimming stage), juvenile (young urchin). Sea urchins are small, globular, spiny sea creatures, composing most of class Echinoidea. They are found in oceans all over the world. Their shell is round and spiny, typically from 3 to 10 cm across. Common colors include black and dull shades of green, olive, brown, purple and red.